The present invention is primarily concerned with the crumb process of manufacturing milk chocolate, although the concepts involved can be utilized in the manufacture of other products which are to be crystallized from a material which is viscous and sticky and for the condensing of a feed stock which becomes viscous and sticky when in its condensed state. The present commercial process of producing milk crumb is described in the book Chocolate, Cocoa and Confectionary: Science and Technology, Bernard W. Minifie, published by The AVI Publishing Company, Inc. (1970), particularly pages 91-93. To summarize, the milk is first evaporated at a temperature of 75.degree. C. to about 30-40% solids in a continuous evaporator. Sugar is added and the milk/sugar mixture is condensed in pans under vacuum at a temperature of about 75.degree. C. to about 90.degree. solids. Chocolate (the term is used herein to include cocoa) liquor is put in heavy mixing equipment, such as a melangeur, and while that equipment is operating a batch of that condensed milk/sugar is gradually run in and kneaded by the equipment. This produces a batch of stiff magma which is placed in shallow trays and vacuum dried at a temperature of 75.degree. - 105.degree. C. This generally is a batch operation although some efforts have been made to use a continuous process.
The present invention is a continuous process wherein all of the ingredients, including the chocolate (which is optional depending upon the desired final product), are initially mixed together to form a liquid feed stock. Essentially the feed stock comprises sugar, milk solids and a substantial amount of moisture (e.g., 28-30% by weight). This feed stock is evaporated in a continuous evaporator to produce a condensed mixture having about 4-6% moisture (by weight) and a temperature of about 121.1.degree. C. (250.degree. F.) to about 126.67.degree. C. (260.degree. F.). The material at this stage is viscous, sticky and ready to crystallize. It has the consistency of a paste (e.g., toothpaste). It is then promptly kneaded and cooled in a continuous operation during which it crystallizes in the form of small particles.
The condensation is performed in a vertical evaporator having an annular, narrow process passageway, both walls of which are heated and scraped. Upon reaching the top of that passageway the material is mechanically moved to the crystallizer and care is taken to maintain the material temperature at about the same as that when it came from the process passageway. The crystallizer also has an annular vertical passageway through which the material moves in the downward direction. This passageway decreases in cross-sectional area between its uppermost and lowermost portions. One of the annular walls that defines this passageway rotates with respect to the other. Both walls carry a plurality of mixing elements that project horizontally into the passageway, with the elements interdigitating in the vertical direction. These perform the kneading operation which is a pulling, stretching and working of the condensed material.
The method and apparatus of the present invention have numerous significant advantages over the present commercial practice. Among these are: based on an equivalent daily production rate, the cost of the apparatus utilizing the present invention is only a fraction of that required for the conventional batch process. Similarly, the required factory space is greatly reduced by the present invention. The present invention does not require that most of the operations be conducted under a vacuum as do the present commercial processes, although a vacuum could be used in the evaporator of the present invention if desired. An increase in uniformity of resulting crumb is achieved. The process in accordance with the present invention is more readily adaptable to a variety of conditions than is the case with conventional operations and thus provides substantial flexibility. The operator can readily produce different products at different times using the same apparatus.
In the manufacture of milk (or chocolate) crumb an important feature is the reaction of the sugar and milk solids during evaporation to produce caramelization. This reaction is an important factor in the flavor of the resulting product. Various manufacturers have different aims as to the flavor to be achieved. Through the use of the present process and apparatus, a manufacturer will have little difficulty in consistently obtaining just the flavor he desires.
In the manufacture of crumb, it is important to form small size sugar crystals. Large crystals are undesirable as they cause difficulties in subsequent processing; they are abrasive to equipment; etc. If crystallization is incomplete an amorphous sugar "glass" is formed which also causes processing difficulties. In the present invention it is possible to substantially eliminate glass from the resulting crumb, which is not always the case with conventional operations.
Further objects and advantages will become apparent from the following description.